Clinical problems in transfusion medicine and hemostasis have rarely been the subject of clinical studies to determine the adequacy of therapy. Common problems such as the appropriate transfusion dose of platelets or fresh frozen plasma (FFP) as well as the optimal therapy for immune thrombocytopenic purpura (IIP) and thrombotic thrombocytopenic purpura (TTP) are not understood. With the creation of the Transfusion Medicine and Hemostasis (TMH) Clinical Trials Network (CTN) a structure has been created to answer these clinical problems. The MGH has served for the past 4 years as a Clinical Core Center (CCC) and has provided much of the senior leadership to the TMH CTN as well as developed half of the protocols currently active. The objectives of this proposal are: (1) To maintain the MGH CCC. We seek to continue to support the Investigators and Research Nurse/Data Coordinator who will design and carry out all study procedures for the TMHCTN clinical trials. We will also maintain the MGH resources and data collection facilities used by the Staff to conduct these studies as well as support the attendance of the Staff at TMH CTN meetings. (2) To support the TMH Fellow. Each year a TMH Fellow is appointed who oversees the clinical trials with the Staff and learns how to conduct clinical trials. (3) To support the TMH CTN trials at the MGH: (a) The SHIP Trial to determine whether FFP will reduce the incidence of hemorrhage in patients with an elevated INR undergoing invasive procedures; (b) The PLADO Trial to determine the appropriate dose of platelets to reduce the risk of bleeding in thrombocytopenic patients; (c) The HOT Trial to assess the rate of thrombosis and complications of therapy for patients with heparin-induced thrombocytopenia (HIT); (d) The STAR Trial to determine the benefit of rituximab added to the usual treatment for TTP; and (e) The trial to assess whether antifibrinolytic treatment reduces bleeding in chronically thrombocytopenic patients. Only through multi-center clinical trials can answers to these problems be addressed. Successful completion of these studies will have a major impact upon the public health in several ways. These studies will significantly alter clinical practice regarding the dose of platelets and FFP to be administered and should result in a major reduction in the costs of transfusion nationwide. They will also establish for the first time the appropriate treatment for uncommon diseases such as HIT, TTP, and chronic thrombocytopenia.